I am looking into building a computer for the first time. I bought a Dell about two years ago, and from what i can tell I could have built a system 10 times as powerful for half as much

Anyways the machine I am looking to build will be used mainly for gaming. I was wondering if I could get some idea's on whats the best of the best. And also how much can i use from my old computer? RAM, Ethernet, etc...
Actually if you know of a site that shows all this that would be just as nice. All the sites I have been able to find are years old, and tell me how to install my Intel Pentium II. I dont really know anything about AMDs, but from what I hear these are the best right now.
Price? I dont really have one. 1000 would be nice but I can go higher. Thanks and all input would be appreciated!